Vertical tail unit for flow control

ABSTRACT

A vertical tail unit (7) for flow control including: an outer skin (13) in contact with an ambient air flow (21), wherein the outer skin (13) extends between a leading edge (23) and a trailing edge (25), and surrounds an interior space (29), and wherein the outer skin (13) includes a porous section (31) in the area of the leading edge (23), a pressure chamber (15) arranged in the interior space (29), wherein the pressure chamber (15) is fluidly connected to the porous section (31), an air inlet (17) provided in the outer skin (13), wherein the air inlet (17) is fluidly connected to the pressure chamber (15), wherein the air outlet (19) is fluidly connected to the pressure chamber (15). The vertical tail unit (7) has reduced drag and an increased efficiency because the air inlet (17) is formed as an opening (35) in the outer skin (13) at the leading edge (23).

RELATED APPLICATIONS

This application is a continuation of Ser. No. 16/153,993 filed Oct. 8, 2018, which claims priority to German Patent Application No. 10 2017 123 440.3, filed Oct. 9, 2017, both of which applications are incorporated by reference in their entirety.

BACKGROUND

The present invention relates to a vertical tail unit for an aircraft. The vertical tail unit is configured for flow control, such as for hybrid laminar flow control. A further aspect of the present invention relates to an aircraft comprising such a vertical tail unit.

The vertical tail unit comprises an outer skin, a pressure chamber, an air inlet, and an air outlet. The vertical tail unit may further comprise a plurality of structural parts, such as stiffeners, for supporting the outer skin from the inside. Further, the vertical tail unit may be composed of a vertical stabilizer and a rudder pivotally mounted to the vertical stabilizer.

The outer skin is in contact with an ambient air flow and extends between a leading edge facing the incoming flow, and a trailing edge. Further, the outer skin has two opposite lateral sides and surrounds an interior space. The outer skin further comprises a porous section in the area of the leading edge for letting air through the outer skin. The porous section might be formed e.g. as a perforated skin panel or as a skin panel made from a porous material.

The pressure chamber is arranged in the interior space for holding an overpressure or an under pressure with respect to the pressure of the ambient air flow in front of the porous section. The pressure chamber is fluidly connected to the porous section.

The air inlet is provided in the outer skin for letting in air from the ambient air flow. The air inlet is fluidly connected to the pressure chamber and configured to cause, in flight of the associated aircraft, an overpressure in the pressure chamber, such that air from the pressure chamber discharges through the porous section to the ambient air flow.

The air outlet is provided in the outer skin for letting out air into the ambient air flow. The air outlet is fluidly connected to the pressure chamber and configured to cause, in flight of the associated aircraft, an under-pressure in the pressure chamber such that air from the ambient air flow is sucked in through the porous section into the pressure chamber. The air outlet may be formed as a movable flap that is or can be opened in the direction of the trailing edge.

Such vertical tail units are known in the art. The air inlet of the known vertical tail units is often formed as an air scoop that projects out of the outer skin into the ambient air flow. However, such an air scoop causes additional drag at the vertical tail unit and decreases efficiency.

SUMMARY OF THE INVENTION

A vertical tail unit has been invented and is described herein that may provide reduced drag an increased efficiency with respect to prior vertical tail units.

This object is achieved in that the air inlet is formed as an opening in the outer skin at the leading edge. The opening might be formed as a hole in the outer skin with a channel following to the inside of the vertical tail unit. In such a way, no parts of the air inlet project out from the outer skin into the ambient air flow so that no additional drag is caused by the air inlet or at least the additional drag is minimized.

According to a first embodiment, the air inlet is arranged at a stagnation point of the leading edge, i.e. at the point where the ambient air flow impinging on the leading edge separates in opposite directions. In such a way, the relatively high stagnation pressure can be used to pressurize the pressure chamber.

According to another embodiment, the air inlet has a circular shape or an oval shape. Such a shape assists for a minimum drag and a maximum pressure in the pressure chamber. However, the air inlet might also have a rectangular shape which is advantageous due to a simple design.

According to another embodiment, the air inlet is arranged further to a root of the vertical tail unit than the porous section. The root relates to that part of the vertical tail unit where the vertical tail unit is or can be connected to a fuselage. In other words, the air inlet is arranged below the porous section. In such a way, the air inlet and the porous section do not interfere one another.

According to a further embodiment, the air inlet is connected to the pressure chamber via an inlet duct. The inlet duct may proceed from the air inlet upwards to the pressure chamber.

In particular, the air outlet may be connected to the pressure chamber via an outlet duct. At least parts of the inlet duct and the outlet duct may be formed integrally as a single piece component. In such a way, a minimum amount of structure and thus weight is required.

According to another embodiment, the air inlet comprises a door for closing the air inlet. The door may be configured to close the air inlet both partly and fully. In such a way, it can be controlled whether and to which extent the ambient air flow can pass through the outer skin into the vertical tail unit.

In particular, the door may be mounted to a hinge, so that the door is pivotable to the inside of the channel when the door is opened. In such a way, no parts of the air inlet project out of the outer skin into the ambient air flow. Further, reliable sealing of the door is enabled.

Further, the hinge may be mounted to a bottom edge or to a top edge of the air inlet with a horizontal hinge axis. In such a way, a symmetric door is enabled that can reliably be sealed.

Alternatively, the hinge may extend centrally across the air inlet. The door includes two door wings mounted to the hinge such that each door wing may cover a part of the inlet opening. In such a way, the air pressure of the ambient air flow in the closed position of the door is divided between the two wings, so that the door wings and actuators can be designed less strong.

In particular, the hinge may have a vertical or horizontal hinge axis. In such a way a symmetric and simple design of the door wings is enabled.

The invention may be embodied in a vertical tail unit of an aircraft. The features and advantages mentioned above in connection with the vertical tail unit also apply for the aircraft.

SUMMARY OF DRAWINGS

Embodiments of the present invention are described in more detail by means of a drawing. The drawings include:

FIG. 1 is a side view of the tail section of an aircraft.

FIG. 2 is a detailed side view of section A in FIG. 1 and shows a first embodiment of an air inlet to be employed in the aircraft shown in FIG. 1 with a bottom hinge and a door in a closed position.

FIG. 3 shows the air inlet shown in FIG. 2 with the door in an opened position.

FIG. 4 shows a detailed side view of section A in FIG. 1 and shows a second embodiment of an air inlet to be employed in the aircraft shown in FIG. 1 with a top hinge and the door in an opened position.

FIG. 5 shows a detailed side view of section A in FIG. 1 and shows a third embodiment of an air inlet to be employed in the aircraft shown in FIG. 1 with a central hinge and two door wings in an opened position.

FIG. 6 is a top view of the air inlet shown in FIG. 5.

DETAILED DESCRIPTION

In FIG. 1 an embodiment of an aircraft 1 according to the invention is illustrated. The aircraft 1 comprises a fuselage 3, a horizontal tail unit 5, and a vertical tail unit 7 according to an embodiment of the invention. The vertical tail unit 7 comprises a vertical stabilizer 9 and a rudder 11 pivotally mounted to the vertical stabilizer 9. The vertical tail unit 7 is configured for hybrid laminar flow control and comprises an outer skin 13, a pressure chamber 15, an air inlet 17, and an air outlet 19.

The outer skin 13 is in contact with an ambient air flow 21 and extends between a leading edge 23 and a trailing edge 25. Further, the outer skin 13 has two opposite lateral sides 27 a, 27 b and surrounds an interior space 29. The outer skin 13 further comprises a porous section 31 in the area of the leading edge 23 for letting air through the outer skin 13.

The pressure chamber 15 is arranged in the interior space 29 for holding an overpressure or an under-pressure with respect to the pressure of the ambient air flow 21 in front of the porous section 31. The pressure chamber 15 is fluidly connected to the porous section 31.

The air outlet 19 is arranged in the outer skin 13 for letting out air into the ambient air flow 21. The air outlet 19 is fluidly connected to the pressure chamber 15 and configured to cause, in flight of the associated aircraft 1, an under-pressure in the pressure chamber 15 such that air from the ambient air flow 21 is sucked in through the porous section 31 into the pressure chamber 15. The air outlet 19 includes a pivotable flap 33 that can be opened in the direction of the trailing edge 25.

The air inlet 17 is arranged in the outer skin 13 for letting air from the ambient air flow 21 into the vertical tail unit 7. The air inlet 17 is fluidly connected to the pressure chamber 15 and configured to cause, in flight of the associated aircraft 1, an overpressure in the pressure chamber 15, such that air from the pressure chamber 15 discharges through the porous section 31 to the ambient air flow 21. The air inlet 17 is formed as an opening 35 in the outer skin 13 at the leading edge 23. The opening 35 might be formed as a hole 37 in the outer skin 13 with a channel 39 following to the inside of the vertical tail unit 7. The air inlet 17 is arranged at a stagnation point 41 of the leading edge 23 and has a circular shape.

As shown in FIGS. 2 to 6, the air inlet 17 comprises a door 43 for closing the air inlet 17. The door 43 is mounted to a hinge 45 such that the door 43 is pivotable to the inside of the channel 39 when the door 43 is opened. In the embodiment shown in FIGS. 2 and 3, the hinge 45 is mounted to a bottom edge 47 of the air inlet 17 with a horizontal hinge axis 49, wherein FIG. 2 shows the door 43 in a closed position and FIG. 3 shows the door 43 in an opened position. In the embodiment shown in FIG. 4, the hinge 45 is mounted to a top edge 51 of the air inlet 17 with a horizontal hinge axis 49.

In the embodiment shown in FIGS. 5 and 6, the hinge 45 extends centrally across the air inlet 17. The door 43 includes two door wings 53 a, 53 b mounted to the hinge 45 such that each door wing 53 a, 53 b may cover a part of the inlet opening 35. The hinge 45 has a vertical hinge axis 49.

As shown in FIG. 1, the air inlet 17 is arranged further to a root 55 of the vertical tail unit 7 than the porous section 31. The air inlet 17 is connected to the pressure chamber 15 via an inlet duct 57 that proceeds from the air inlet 17 upwards to the pressure chamber 15. The air outlet 19 is connected to the pressure chamber 15 via an outlet duct 59. Wide parts of the inlet duct 57 and the outlet duct 59 are formed integrally.

While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority. 

The invention is:
 1. A vertical tail unit for flow control, comprising an outer skin configured to contact an ambient air flow, wherein the outer skin extends between a leading edge and a trailing edge, and the outer skin surrounds an interior space, and wherein the outer skin comprises a porous section in an area of the leading edge, a pressure chamber arranged in the interior space, wherein the pressure chamber is fluidly connected to the porous section, an air inlet provided in the outer skin, wherein the air inlet is fluidly connected to the pressure chamber and configured to cause an overpressure in the pressure chamber such that air discharges through the porous section into the ambient air flow, wherein the air inlet is formed as an opening in the outer skin at the leading edge, an air outlet duct including an air outlet provided in the outer skin, wherein the air outlet is fluidly connected via the air outlet duct to the pressure chamber and configured to cause an under-pressure in the pressure chamber such that air of the ambient air flow is sucked in through the porous section, and an inlet door configured to close the air inlet, wherein the inlet door is mounted to a hinge within the leading edge so that the door opens by pivoting inward relative to the leading edge to create the overpressure in the pressure chamber, wherein the air inlet is aligned with a stagnation point on a leading edge of the vertical tail unit, and an outlet door configured to close the air outlet duct, wherein the outlet door opens to create the under-pressure in the pressure chamber which causes the ambient air to flow through the porous section and into the pressure chamber.
 2. The vertical tail unit according to claim 1, wherein the air inlet is on the leading edge at a location separate from the porous section.
 3. The vertical tail unit according to claim 1, wherein the air inlet has a circular shape or an oval shape.
 4. The vertical tail unit according to claim 1, wherein the air inlet is closer to a root of the vertical tail unit than to the porous section.
 5. The vertical tail unit according to claim 1, wherein the air inlet is connected to the pressure chamber via an inlet duct.
 6. The vertical tail unit according to claim 5, wherein the air outlet duct extends from the air outlet to the pressure chamber.
 7. The vertical tail unit according to claim 6, wherein parts of both the inlet duct and the outlet duct are a single piece component.
 8. The vertical tail unit according to claim 1, wherein the air inlet comprises a door for closing the air inlet.
 9. The vertical tail unit according to claim 8, wherein the door is mounted to a hinge so that the door is pivotable to the inside when the door is opened.
 10. The vertical tail unit according to claim 9, wherein the hinge is mounted to a bottom edge or to a top edge of the air inlet and the hinge has a horizontal hinge axis.
 11. The vertical tail unit according to claim 9, wherein the hinge extends across the air inlet, and the door includes two door wings each mounted to the hinge such that each of the two door wings pivots about the hinge and the two door wings cover the inlet opening while the door is closed.
 12. The vertical tail unit according to claim 11, wherein the hinge has a vertical hinge axis.
 13. An aircraft comprising a vertical tail unit according to claim
 1. 14. A vertical tail unit for an aircraft comprising an outer skin configured to contact ambient air flowing over the aircraft during flight, wherein the outer skin forms a leading edge and includes opposite lateral sides extending from the leading edge towards a trailing edge of the vertical tail unit, wherein the outer skin comprises a porous section of the leading edge; an interior volume within the outer skin; a pressure chamber in the interior space fluidly connected to the porous section, an air inlet in the outer skin at the leading edge, wherein the air inlet is fluidly connected to the pressure chamber and configured to cause an overpressure in the pressure chamber such that air discharges from the pressure chamber, through the porous section and into ambient air flowing over the porous section, wherein the air inlet is at the leading edge of the vertical tail unit and aligned with a stagnation point on the leading edge; an inlet door configured to close the air inlet, wherein the inlet door is mounted to a hinge proximate the leading edge and the inlet door is pivotable about the hinge to cause a trailing edge of the inlet door to move inside the leading edge to create the overpressure in the pressure chamber; an air outlet duct fluidly connected to the pressure chamber and configured to cause an under pressure in the pressure chamber such that ambient air flowing over the porous section is sucked in through the porous section and into the pressure chamber, and an outlet door configured to close the air outlet duct, wherein the outlet door opens to create the under-pressure in the pressure chamber which causes the ambient air to flow through the porous section and into the pressure chamber.
 15. The vertical tail unit according to claim 14, wherein the air inlet is on the leading edge at a location separate from the porous section.
 16. The vertical tail unit according to claim 14, wherein the air inlet is closer to a root of the vertical tail unit than the porous section.
 17. The vertical tail unit according to claim 14, wherein the air inlet is on a portion of the leading edge oriented at an angle from vertical which is greater than an angle from vertical of the porous section.
 18. The vertical tail unit according to claim 14, wherein the inlet door is mounted to the vertical tail along a horizontal hinge axis.
 19. The vertical tail unit according to claim 14, wherein the hinge extends across the air inlet, and the inlet door includes two door wings each mounted to the hinge, wherein the two door wings pivot about the hinge to close and open the inlet opening.
 20. The vertical tail unit according to claim 17, wherein the inlet door is attached to the vertical tail unit by a hinge having a vertical hinge axis. 